1. Field of the Invention
The present invention relates to an image processing apparatus, such as a color copying machine and a color FAX, for processing color image signals to record a color image using recording materials (such as ink toners) of plural colors.
2. Related Background Art
When color recording is performed by the additive color mixture based on image signals obtained through color separation, generally that black lines and characters, in particular, are recorded by superposing recording materials of three colors, i.e., Y, M and C, or four colors, i.e., Y, M, C and K.
However, the superposition of recording materials of those three or four colors raises the following problems:
(1) The resulting color by the superposition does not look perfectly black,
(2) Difficulties in high-accurate superposition causes a color shear or offset, which also makes the resulting color not look black, and
(3) In recording based on the pseudo-half-tone processing, the recording cannot be made by arraying dots in a continuous linear line. Thus, an image cannot be represented with high resolution. Meanwhile, it has been previously proposed in U.S. patent application Ser. No. 378,488, now U.S. Pat. No. 5,029,227 a method of representing a monochromatic image by discriminating and separating portions of lines and characters in an image from other image portions of half tone, and recording only the former portions with high resolution, thereby allowing both gradation and resolution of the image to stand together in representation.
Although this method can solve the above problem (3), it has a shortcoming to require independent hardwares for different colors when applied to processing of a color image. Further, a method of discriminating a black portion from color signals and judging a region which coincides with a character portion extracted from the component of one color, e.g., the G component, as a black character region still accompanies the problems that the black portion is difficult to discriminate inexpensively with high accuracy, and that the judged black region is not always precisely coincident with the actual black region. In addition, the so-called black signal produced by masking or that black signal is adapted to correct only black portions which can be represented by using C, M and Y, and thus has not a sufficient level for line portions of black characters, in particular. To solve the above problems, U.S. patent application Ser. No. 173,654, U.S. Pat. No. 4,958,219, U.S. patent application Ser. No. 327,098, now U.S. Pat. No. 5,047,844, U.S. patent application Ser. No. 367,673, now U.S. Pat. No. 5,031,034 and U.S. patent application Ser. No. 519,500, now U.S. Pat. No. 5,113,252, have been proposed, but there still remains room for improvement.
Furthermore, it is conventional in image processing apparatus that a color image is subjected to color separation Into three colors, i.e., R, G and B, and C, M, Y and K (black) signals are then produced as record colors, followed by the pseudo-half-tone processing for each of the four colors. As a pseudo-half-tone processing technique, while there is known for many years a dither method which can be constituted inexpensively, a data storage type technique represented by an error dispersing method has become more popular in recent years which carries out error correction through re-quantization for enabling resolution and gradation to be reproduced in a substantially compatible manner.
In the above pseudo-half-tone processing technique of data storage type (i.e., the conditioned dither method), however, re-quantized dots are not directly determined from input data of one point. For the reason, when input image data obtained through color separation into four colors are processed independently, the re-quantized dots in four colors may locally overlap with each other. Accordingly, in the case that recording is made using the electrostatic process based on the re-quantized data, for example, toners of four colors locally overlap with each other to form a projection with the height of several 100 microns on the sheet surface of transfer paper, resulting in drawbacks of lowering a fixing property and degrading an image quality.
In the case of recording an image by an ink jet technique, for example, a large amount of ink is jetted into a local area. This results in similar drawbacks that an ink smear occurs on the rear side of recording paper and a longer period of time is required for drying.
In addition, when deposit positions of recording materials of different colors are not perfectly coincident with each other for each pixel by virtue of limitations in mechanical accuracy, a color shear is caused and color reproducibility is badly deteriorated.
The present invention has been accomplished in view of the problems as stated above, and has for its object to provide an image processing apparatus which can satisfactorily reproduce a color image, particularly, a black color line in the color image.
To achieve the above object, the present invention discloses an image processing apparatus comprising first judgment means for judging whether or not a pixel of interest belongs to a black line image portion, and outputting a first judgment signal indicating a judgment result, second judgment means for judging whether or not pixels in the vicinity of said pixel of interest belong to a black line image portion, and outputting a second judgment signal indicating a judgment result, and control means for controlling recording of said pixel of interest based on the first and second judgment signals outputted from said first and second judgment means.
Also, there is disclosed an image processing method comprising a first judgment step of judging whether or not a pixel of interest belongs to a black line image portion, a second judgment step of judging whether or not pixels in the vicinity of said pixel of interest belong to a black line image portion, and a control step of controlling recording of said pixel of interest based on judgment results in said first and second judgment steps.
Another object of the present invention is to provide an image processing apparatus which has a simplified circuit configuration.
To achieve that object, the present invention discloses an image processing apparatus comprising m-value coding means for coding a plurality of color component signals, each in n bits, one by one into any value ranging from 0 to m (where 2xe2x89xa6m less than n), Judgment means for judging whether or not an image represented by said plurality of color component signals belongs to a black line image portion, and control means for controlling, based on a judgment result by said judgment means, recording with a plurality of color component signals which have been coded by said m-value coding means into any value ranging 0 to m.
Still another object of the present invention is to provide an image processing apparatus suitable for high-speed processing and real-time processing.
To achieve that object, the present invention discloses an image processing apparatus comprising means for binary-coding a plurality of color component signals color by color, means for removing minor color components from said color component signals, and means for generating record color signals by using both the color component signal left after removing said minor color components and said color component signals before the binary-coding.
Yet another object of the present invention is to provide an image processing apparatus which has satisfactory color reproducibility.
To achieve that object, the present invention discloses an image processing apparatus comprising detecting means for detecting a black line image portion in an input color image, and generating means for generating record signals to record the black line image portion, detected by said detecting means, by superposing multiple dots including a black dot.
Also, there is disclosed an image processing method comprising the steps of detecting a black line image portion in an input color image, and generating record signals to record said black line image portion by superposing multiple dots including a black dot.
Other objects and modes of the present invention will be apparent from the following explanation with reference to the attached drawings and the description of claims.